WWDM Transceiver Update and 1310 nm eye-safety Brian E. Lemoff and Lisa A. Buckman Hewlett-Packard Laboratories lemoff@hpl.hp.com IEEE 802.3 HSSG Meeting Montreal, Quebec July 5-9, 1999
Overview I. Review of HP WWDM Proposal II. Demultiplexer results III. Crosstalk results IV. Multimode link results V. 1310nm eye-safety
Data Fiber Package Sources Wvlngth MUX HP WWDM Proposal 4 duplex channels, 2.5 Gb/s/channel Dual use SMF/MMF (SM TX, MM RX) MTRJ duplex connector, BGA surface mount Uncooled, unisolated DFB, No SMSR spec 1280,1300,1320,1340 nm 4-to-1 silica waveguide combiner Detectors InGaAs PIN photodiode array DEMUX ICs Compact molded plastic bulk zigzag 4-channel TX; 4-channel RX (integrated)
HP Labs WWDM MTRJ Prototype MTRJ Connector RX TX Ball Grid Array FR4 PCB Brian Lemoff and and Lisa Buckman/ Optical Comm. & Meas. Dept.
Assembled WWDM MTRJ Module
Wavelength Demultiplexer Three views of ray tracing in wavelength demultiplexer
Wavelength Demultiplexer
Demultiplexer Transmission Spectrum First results using home-grown interference filters Transmission (db) 0-1 -2-3 -4-5 -6-7 -8-9 -10-11 -12-13 -14-15 -16-17 -18-19 -20 1260 1270 1280 1290 1300 1310 1320 1330 1340 1350 1360 Wavelength (nm)
4-channel Transmitter IC
TX Interchannel Crosstalk Performance Measured with external RX; 2.488 Gb/s 2 7-1 PRBS Single TX channel on, others off -3-4 one laser on all lasers on log BER -5-6 -7 All 4 channels on -8-9 -10-30 -29-28 -27-26 -25 Received Optical Power (dbm) BER curves show no power penalty for single channel vs. four channels on TX.
TX Interchannel Crosstalk at 3.125 Gbaud One channel on, three off 3.125 Gb/s PRBS extinction 8.4 db All four channels on 3.125 Gb/s PRBS extinction 9.0 db
12-Channel RX IC - Using 4 channels Soon-to-be available 4-channel IC will greatly reduce RX footprint
TX-to-RX Crosstalk at 2.488 Gb/s No power penalty is observed in RX due to 4-channel TX data -3-4 TX data on TX data off TX data and supply off log BER -5-6 -7-8 -9-10 -26-25 -24-23 -22-21 -20-19 -18-17 -16 Received Optical Power (dbm)
Multiplexed Spectrum Using multimode polymer waveguide combiner -20 Power (dbm) -30-40 -50-60 -70 1260 1280 1300 1320 1340 1360 Wavelength (nm)
SpectraLAN-LX Link Results: 300 m MMF 1340 nm 2.488 Gbaud/channel 1320 nm 2^7-1 PRBS Multimode Polymer Mux Injection-molded demux 1300 nm Total launch power: -2 dbm 1280 nm
Class 1 Eye Safety At 1310nm, in SMF, FDA/CDRH is more restrictive than IEC FDA Center for Devices and Radiological Health 21 CFR Ch1 (4-1-98 Edition), sec. 1040.10 guidelines specify that for Class 1: No more than 0.195 mw of average power may pass through an aperture 7 mm in diameter at a distance of 20 cm from the end of the fiber. Aperture Fiber 7 mm Power Meter 20 cm
Class 1 Eye Safety - (cont d) According to Corning spec., SMF mode field diameter is between 8.8 µm and 9.8 µm. Thus use 9.8 µm as worst case (i.e. lowest NA). Assume gaussian beam. Waist (1/e 2 intensity radius) = 4.9 µm at fiber tip. At 20 cm, we have: w( z) = λz πw 0 = (1310 nm) (20 cm) (3.1416) (4.9 µ m) = 17 mm 2 2P -2r I ( r) = exp exp 0069 r 2 2 w w π ( 2-0. )
Class 1 Eye Safety - (cont d) The fraction of power passing through a 7mm aperture is: 2 η = 2 πw a 2πr 2r exp w 0 2 2(3.5 mm) η = 1 exp 2 (17 mm) 2 2 dr 2a = 1 exp 2 w = 0.081 2 Thus, allowed Class 1 fiber power, is P = 0.195 mw 0.081 = 2.41mW = + 3.8 dbm P = + 4.7 dbm (Note: For 8.8 µm mode field diameter,.)
Why is there confusion? A limit of +2dBm is often cited Lucent Technical Note: Laser Safety and Optical Fiber Communications Systems, March 1999 computes a +2dBm Class 1 eye-safety limit. The authors followed the identical calculation, but took Mode Field Diameter to mean 1/e intensity, rather than 1/e 2 intensity, as it is normally defined. They also assumed 8.8µm as MFD. Question: What is largest MFD allowed and how accurate is the gaussian model in predicting eye-safety? Thanks to Richard Booman and Scott Lowrey of Network Elements for bringing this Lucent Technical Note to my attention.
Eye Safety and WWDM Power Budget should allow 4-channel eye-safe operation Eye-safe limit at 1300 nm: +3.8 dbm Limit per channel: -2.2 dbm Demultiplexer loss: <6 db (worst case) Link Budget: <8 db (expected) Required receiver sensitivity <-16.2 dbm Several db of margin remains with existing Si IC technology. Next generation IC s will have even more margin.